This invention relates to a spectrophotometer which can be used selectively as a single-beam and a double-beam spectrophotometer.
In a typical double-beam spectrophotometer, the monochromatic light beam emerging from a monochromator is divided into two beams commonly referred to as the reference and sample beams by use of a rotating chopper mirror.
Since the two beams are chopped, it is impossible to measure a sample which changes more rapidly than the chopping cycle. For example, if the chopping cycle is 60 Hz, it is impossible to measure a sample which changes materially within a period of about 17 milliseconds.
Therefore, for measurement of such rapidly changing samples a single-beam spectrophotometer without any rotating component such as a chopper is used. However, to have two types of spectrophotometers ready for use at hand requires a high cost for installation and maintenance, and it is troublesome to selectively use two types of instruments.